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Title:Ab initio investigations of the excited electronic states of caoca
Author(s):Fawzy, Wafaa M.
Contributor(s):Heaven, Michael
Subject(s):Theory and Computation
Abstract:Chemical bonding in alkaline earth hypermetalic oxides is of fundamental interest. Previous Ab initio studies of CaOCa predicted a centrosymmetric linear geometry for both the $^{1}\Sigma_{g}^+$ ground state and the low lying triplet $^{3}\Sigma_{u}^+$ state\footnote{B. Ostojic{\'i}, P.R. Bunker, P. Schwerdtfeger, Artur Gertych, and Per Jensen, Journal of Molecular Structure 1023 (2012) 101–107.}. However, there have been no reports concerning the higher energy singlet and triplet states. The present work is focused on characterization of the potential energy surface (PES) of the excited $^{1}\Sigma_{u}^+$ state (assuming a centrosymmetric linear geometry) and obtaining predictions for the $^{1}\Sigma_{u}^+\leftarrow^{1}\Sigma_{g}^+$ vibronic transitions. We employed the multireference configuration interaction (MRCISD) method with state-averaged, full-valence complete active space self-consistent field (SA-FV-CASSCF) wavefunctions. In these calculations, the active space consisted of ten valence electrons in twelve orbitals, where all the valence electrons were correlated. Contributions of higher excitation and relativistic effects were taken into account using the Davidson correction and the Douglas-Kroll (DK) Hamiltonian, respectively. The correlation-consistent polarized weighed core-valence quadruple zeta basis set (cc-pwCVQZ-DK) was used for all three atoms. The full level of theory is abbreviated as SA-FV-CASSCF (10,12)-MRCISD-Q/cc-pwCVQZ-DK. The calculations were carried out using the MOLPRO2012 suite of programs. For the centrosymmetric linear geometry in all states, initial investigations of one-dimensional radial cuts provided equilibrium bond distances of 2.034 {\AA}, 2.034 {\AA}, and 1.999 {\AA} for the $^{1}\Sigma_{g}^+$ , $^{3}\Sigma_{u}^+$ , and $^{1}\Sigma_{u}^+$ states, respectively. The vertical excitation frequency of the $^{1}\Sigma_{u}^+\leftarrow^{1}\Sigma_{g}^+$ optical transition was calculated to occur at 14801 \wn . These predictions were followed by spectroscopic searches by Heaven et al. Indeed, rotationally resolved vibronic progressions were recorded in the vicinity of the predicted electronic band origin. Calculation of the three-dimensional PES showed that the potential minimum in the $^{1}\Sigma_{u}^+$ corresponds to a bent equilibrium geometry with a bond angle of $120^{\circ}$ (C$_{2v}$ point group, where the electronic symmetry is $^{1}A_{1}$). This result suggests that the Ca-O bonds in CaOCa possess covalent character in the $^{1}A_{1}$ excited state and ionic character in the $^{1}\Sigma_{g}^+$ ground state. The current results, as well as those from ongoing studies will be presented.
Issue Date:2016-06-21
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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